The present invention relates to a sensor arrangement designed for detecting and reporting to a higher level controller a safe installation state of an automatically operated installation.
DE 103 37 660 A1 discloses a sensor arrangement having an input circuit in the form of a so-called receiving head which is able to receive different input signals. The different input signals come from a plurality of transponders, each transponder emitting an individual identification signal when it enters the vicinity of the receiving head. An evaluation unit can use the identification signals to decide which transponder is in the vicinity of the receiving head at a particular time. The known sensor arrangement is used, in particular, to detect various operating positions of a movable part. In one example, the transponders are arranged on the lateral edge of a rolling door. Depending on the open or closed position of the rolling door, the receiving head receives a different transponder signal as an input signal. The evaluation unit can use the received transponder signal to determine the open or closed position of the rolling door and, on the basis thereof, can generate a control command for a motor control unit which is used to open or close the rolling door.
Controlling the rolling door on the basis of the detected position is a typical example of an automated process in which mechanical parts are moved. There are many cases in which the parts must be moved with a particular degree of accuracy. It is therefore necessary to determine the instantaneous position and/or other movement variables, for instance the movement speed. Any faults may disrupt the desired operating procedure. During the automated production of products, faults may affect, in particular, the product quality and/or the productivity.
In addition, there are cases in which the operating position of a movable part is relevant to safety, for instance in the case of a guard door which closes access to a dangerous machine. In such a case, it must be ensured that the machine cannot be activated if the guard door is open. Here, the accuracy of the position determination does not play a role as long as the closed guard door is reliably detected. On the other hand, a fault in the sensor arrangement must not, under any circumstances, result in the machine being able to be activated when the guard door is open.
From these different requirements, sensor arrangements and controllers have been developed either for the normal operating procedure of an automated installation or for safeguarding a dangerous machine. In practice, a distinction is often made between so-called standard applications, which relate to the usual operating procedure of an automated installation, and fail-safe applications which are primarily used to protect against dangerous machine movements or the like. Since a fault in a fail-safe application may endanger the health or even the life of persons, while faults in a standard application “only” affect the quality of products and/or the installation productivity, components and devices for fail-safe applications require special approval from supervisory authorities, which approval is only given if the intended safety function is also ensured in the case of any conceivable fault. Components for fail-safe applications therefore require a remarkably higher amount of design effort in order to achieve the required fail-safety in comparison with components and devices for standard applications. In addition, any change to a device or a component for a fail-safe application must be tested again by the supervisory authority since the change might be the cause of the loss of the required safety function in the event of a fault.
On account of the higher requirements imposed on fail-safety, a distinction has been made to date between devices and components for standard applications and devices/components for fail-safe applications. However, the sensor arrangement from DE 103 37 660 A1 mentioned above makes it possible to combine a standard application (namely determination of the current operating position of the rolling door in order to control movement) with a safety function (namely fail-safe detection of the completely closed door). In order to maintain separation between standard application and fail-safe application, DE 103 37 660 A1 proposes an evaluation unit which internally has a standard part and a separate fail-safe part. The input signals from the different transponders are supplied to the parts in a parallel manner. However, the output signals from the evaluation unit are clearly separate for standard applications and fail-safe applications.
The known sensor arrangement therefore makes it possible to use a single sensor part which is designed to receive different identification signals, with one of the identification signals being a safety-relevant signal for a fail-safe application, while the other signals are standard signals for controlling an operating procedure in a manner which is not relevant to safety.
DE 10 2004 020 997 A1 discloses a sensor arrangement which is exclusively intended for fail-safe applications. This known sensor arrangement also has an input circuit for receiving a signal which comes from a transponder. The sensor arrangement has a redundant design and has two microcontrollers which monitor one another. Two switching elements generate redundant output signals. This sensor arrangement can be used to monitor the closed position of a guard door, with the redundant output signals only together signaling the safe closed position of the guard door. A similar two-channel sensor arrangement for fail-safe applications is disclosed by EP 0 968 567 B2.
DE 103 34 653 A1 discloses another sensor arrangement for monitoring a guard door in a fail-safe manner. In this case, a switching element is arranged in the input circuit for receiving the signal from a transponder, which switching element can selectively be used to suppress the input signal from the transponder. The switching element thus enables regular functional tests which ensure fault-free operation of the sensor.